1. Technical Field
In its most general aspect, the present invention relates to the industrial field of micro fuel cells, supplied with hydrogen, for generating electric energy, particularly but not exclusively intended for the operation of portable electronic devices.
In particular, the present invention relates to a process and a corresponding apparatus for continuously producing gaseous hydrogen to be supplied to micro fuel cells of the above type.
2. Description of the Related Art
It is known that the growing demand for electric energy to supply portable electronic devices has determined an intense, strong interest of the experts of the field in the identification, design and realization of new electric energy sources, in addition to and overcoming the traditional batteries used to date for the above scope, for example lithium ions batteries.
It is known that, among the new portable electric energy sources, great interest has been aroused by miniaturized fuel cells, hereafter indicated as micro cells, i.e., those devices capable of obtaining electric energy from a suitable fuel, for example through oxidation-reduction reactions.
In substance, micro cells are essentially energy converters which, by exploiting the energetic content of a chemical fuel, for example through an oxidation-reduction reaction, allow to produce electric energy in a reversible way, supplying collateral reaction products, in particular heat and water.
It is also known how, for some time, the researchers' attention to this industrial field is aimed at the identification of fuels which, suitably processed in respective micro cells, allow an easy, clean obtainment of electric energy, with high performances.
At present, hydrogen and methanol are the preferred fuels for the processing in micro cells of the considered type, in particular of the polymeric solid electrolyte type (Proton Exchange Membrane Fuel Cells).
The density of the power generated by these micro fuel cells, main requisite in portable applications, is strongly influenced by the type of fuel used.
It has been proved that this density of energy obtainable from a micro fuel cell supplied with hydrogen is, under the same conditions, higher by some orders of magnitude than the one obtainable from a similar micro cell supplied with methanol. Hydrogen is thus prima facie the fuel to be used in micro fuel cells for generating a high power density, like in the case of portable applications.
But is has also been proved that for obtaining, from a micro hydrogen cell, amounts of electric energy sufficient for a satisfying, prolonged operation of a respective portable electronic device, in particular amounts of energy sufficient for justifying a gradual substitution of the batteries currently used as portable energetic sources, it is necessary that said micro cell avails itself of a considerable hydrogen “reserve”.
For the above purpose, and having taken into account the hydrogen production techniques used up to now, the very reduced dimensions of the portable electronic devices considered, such as those of the micro fuel cells associated with said devices, the above need can be satisfied by using small tanks (cylinders) wherein the hydrogen is stored at a gaseous state under very high pressures, or even liquefied at very low temperatures.
Known technical solutions for storing hydrogen compress hydrogen in the gaseous phase under high pressure, for example, equal to 200-350 bar at a temperature of 20° C. It is also known to store hydrogen in the liquid form at very low temperatures, for example, at −253° C. under a pressure of one bar.
The operative conditions (of temperature and pressure) for the storage of hydrogen in the liquid and gaseous forms realized according to the prior art can be summarized in the following table:
Storage systemTemperature (° C.)Pressure (bar)liquid H2−2531compressed H220200-350
Besides the known risk of highly dangerous manipulations of the hydrogen stored in small tanks under the above conditions, other drawbacks of the known techniques are exactly due to the fact that these manipulations must be carried out between the hydrogen production step and the step of its transformation into electric energy, involving respective methodologies, apparatuses and devices of difficult management and control. Moreover, as regards the hydrogen liquefaction, it is known that it implies a total loss of energy equal to 30%, since for maintaining the hydrogen in the liquid form it is necessary to preserve it at a temperature of −253° C. Moreover, for the conversion of the hydrogen into the liquid form, the prior art uses cryogenic containers which, besides being expensive instruments, require a reduction of the leaks of fuel through evaporation to the minimum.
For these reasons, the use of hydrogen as an energetic source in portable commercial systems has not yet found that great, advantageous widespread uses despite its potentials.